1. Technical Field
The present invention relates to an optical device and an exposure apparatus, and more particularly, to an optical device and an exposure apparatus which connect optical members such as optical fiber and transparent member to each other to propagate light such as laser light.
2. Related Art
As a conventional optical device which connects optical members such as optical fiber and transparent members with each other to propagate laser light, International Patent Application Laid-open No. WO2004/68230 discloses a technique in which a coreless fiber is connected to an output terminal of fiber by fusion splice, and a length of a light path is set such that output beams are not vignetted by coreless fiber end. Especially when the coreless fiber length is set to 1 mm or less, vignetting is reduced.
Japanese Patent Application Laid-open (JP-A) No. 5-288967 discloses a device in which a light-introduction rod having the same refractive index as that of a core of optical fiber and having the same outer diameter as that of the optical fiber is integrally formed on an input terminal face of the optical fiber by heating fusion.
JP-A No. 2007-25431 discloses a pigtail type laser module in which light power density in a fiber incident terminal face or output terminal face exposed to air is 15 W/mm2 or less or 60 to 800 W/mm2.
JP-A No. 2006-286866 discloses a receptacle type laser module in which a transparent member is brought into contact with a fiber incident terminal face to collect semiconductor laser light from the transparent member and the light is introduced into the optical fiber, and light density on the incident side of the transparent member is 10 W/mm2 or less.
However, when the technique described in International Patent Application Laid-open No. WO2004/68230 is used in an incident portion of the pigtail type laser module, there is a problem that if light output is high, coreless fiber end is contaminated in some cases and its lifetime is reduced. When the technique is used for a receptacle type laser module, on the other hand, the optical fiber is abutted against a transparent member such as a stab, thereby positioning the fiber end in the beam propagating direction. However, when the light output is high, fusion occurs between the coreless fiber and the stab while laser light is on. In this case, there was a problem that the fused portion is easily peeled off by vibration or the like, and connection loss to the optical fiber is increased.
According to the technique described in JP-A No. 5-288967, like the technique of International Patent Application Laid-open No. 2004/68230, if the light output is high when the technique is used for the receptacle type laser module, there is a problem that the fusion occurs and the connection loss to the optical fiber is increased. When the incident light output is high, there was another problem that the fiber terminal face is contaminated.
According to the technique described in JP-A No. 2007-25431, in a fiber incident terminal face or output terminal face, if the light density exceeds 15 W/mm2, contamination may not be prevented however, there was a problem that since the core diameter of the fiber incident terminal is determined, the upper limit of the light output is determined by the fiber diameter and thus, it is impossible to make the light output be considerably high.
According to the technique described in JP-A No. 2006-286866, like the technique of International Patent Application Laid-open No. 2004/68230, there was a problem that the fusion occurs and the connection loss to the optical fiber was increased.
When a light source of short wavelength such as 405 nm is used, it is known that contamination is generated in fiber end, light output is reduced and film quality is deteriorated. It is known that especially when the light output density becomes high, a surface of a transparent member such as a glass that is in contact with air is contaminated and output is largely lowered.
To suppress the reduction in light output caused by such contamination, it is conceived to lower the light output density however, in the conventional technique, it is unclear as to how much the light output density should be lowered to suppress the reduction in light output caused by contamination.
When high output light enters in the structure in which the transparent member is connected to the fiber end as mentioned above, it is possible that fusion of glasses occurs on both terminal faces. However, if fusion occurs, there is a possibility that they are peeled off even with slight vibration applied to the optical fiber, and there is a problem that transmission loss is increased due to light scattering caused by unevenness on the peeled surface, and the reliability is deteriorated.